Propellant grains formerly have been of uniform cross sectional configuration throughout the length of the grain. These former propellant grains burned with excessive erosion of the after end resulting in an uneven power output and eventually burning the motor tube itself. When insulation has been used to prevent damage to the casing, the space available for propellant has thus been reduced and the fuel-to-weight ratio has likewise been reduced.
According to the present invention, a propellant grain is formed with a novel cavity configuration resulting in improved burning with more even power distribution and eliminating the need for heavy insulation of the after end of the motor.